Method of reducing evaporation losses



Aug. 27, 1946. n P. J. HARRINGTON I 2,406,540

METHOD OF REDUCING EVAPORAYTION `LSSES u Filed Aug. 19, 1945 Patented Aug. 27, 1946 METHOD oF REDUCING EvAPoRATIoN p LossEs Paul J. Harrington, Mountainside, N; J., assignor to Standard Oil Development poration of Delaware Application August 19, 19,43, Serial No. 499,256 i 5 Claims. (Cl. 220-85) 1 This invention relates to equipment for storing Volatile liquids in bulk and in particular to a method of reducing evaporation losses in tanks containing relatively 4volatile petroleum liquids. In the storage of large Volumes of Volatile liquids, particularly evident expansive and contractive effects in'the vaporv space occur as the result of vdaily changes in weather conditions. This breathing ofthe tank is particularly marked in climates and during seasons in which marked diierences occur between day and night temperatures. In the'prior art` the eiect has been considered inthe building of tanks of many types of construction to care for either withstanding the pressure changes-or various means of absorbing the volume and changes in additional equipment as in balloons or gas plants. The present invention is a departure from such type corrective measures in employing controlled amount-s of condensing steam in the vapor space as a means of maintaining relatively uniform temperature and pressure conditions despite changes in the surrounding atmospheric conditions. I g

Thus'the invention contemplates any means by which controlled supply of heat is furnished to the vapor space in storage equipment for relatively volatile liquids throughV the medium of condensing steam in order to maintain the temperature and incidentally the pressure when the tank is not heated by the rays of the sun during a portion of each day. When the heat input from the sun to the vapor space is at a maximum almost no steam is being introduced into the vapor space. During the colder part of the dalr when there would be a heat loss from the tank, steam is supplied to the vapor space to furnish Company, a cored by steam admitted through line 20 vto approximately the maximum temperature which is expected to be encountered for a given season of the year or other period between manual adjustments; any vapor expelled in ysuch an adjustment passing out through valve 22. When the temperature is falling surrounding the tank,

there is a tendency for the vaporV space to lose heat to prevent the cooling and contraction of\ the Vapor space which, if permitted to take place,

would result in a reduction in pressure and inltration of air. Also to be considered within the concept of the invention is that when an inert gas is also employed in the vapor space and use made of condensing steam in order to maintain relatively uniform temperature and pressure conditions. Thus the use in conjunction with an inert gas blanketing system is an alternative use of the invention.

A typical embodiment of the invention is diagrammatically represented in the accompanying drawing in which a pressure controller system I IJ with a sensitive temperature element I2 is connected to the Vapor space I4 of a cone-roof tank I 6 supplied with a voltaile liquid by means of filling line I8. The vapor space is initially heatheat and -to contract Initiation of contraction, however, tends to establish `a vacuum` on the tank. This may beV allowedto proceed to the point where additionalvacuum would openthe vacuum release valve`i24 and allowair to enter into the'vapor space. Before this latter point is attained, however, the pressure controller system I0' is set so as to admit steam through line 20`fdirectly into the vapor space of the tank. In the "tank, the steam condenses giving up its latent'heattoV warmthe Avapors in the tank and produce lan expansion to prevent theintake of air from the atmosphere. The condensed water sinks through-the hydrocarbon product to the bottom ofthe tank'whereV water from atmospheric condensation and other sources is always present and'l may' be drawn oi through line '26 from time to time. When the addition of steam has raised the temperature of the tank contents to such a degree that the pressure in the vapor space has increased almost to the setting of the pressure valve 28 on the vapor space, the pressure controller system I0 can be made to cutoff the steam supply by means of the valve system 30. Under these conditions, the amount of steam iiowing into the vapor space will be such as to balance the pressure between the setting of the vacuum and pressure valves 24 and 28 respectively on the tank and no air will thus be 4drawn into the tank or discharged from it despite changes in external weather conditions.

The advantages of protecting the product or minimizing the product loss are evident from the above description. Compared with other means of accomplishing the same end, the proces-s proposed is much cheaper than changing tanks to floating roofs, and the providing of vapor balloons, etc. Almost no investment cost is involved to equip existing tanks with the system and the operating costs per year under average conditions have been estimated at only a few hundred dollars to effect a saving inthe case of gasoline amounting to several thousand dollars.

The invention may be applied practically in the case of cone-roofs which are undergoing evaporation losses but which cannot economically be taken care of by existing systems. Thus a rect heat exchanger may be employedrather than injecting steam directly into the' vapor space.

The invention now specically illustrated, what is claimed is:

1. The method of reducing evaporation losses in closed storage equipment containing relatively Vvolatile liquids which comprises rst heating the closed vapor space just above the maximum temperature to which the storage equipment is to be exposed, then exposing the system to the tempera-tures cf the atmosphere and passinginto the vapor space steamv in amounts so controlled by the. vapor temperature as to maintain relatively uniform temperature conditions in the vapor space and to prevent an excessive pressure drop in the vapor space due to decreasingatmospheric temperatures. f

y2; The method aecordingitc claim 1 in which the amountr of steam admitted varies inversely y with the press-ure in said vapor space.

3. In closed storage. equipment containing relatively volatile liquids and exposed to the tempery ature of theatmosphera the method of reducingevaporation losses, which comprises first heatV ing the closed vapor space just above the maximum temperature to whichthe storage. equipment is to be exposed, and then passing steam into the vapor space in amount so controlled by the vapor temperature as to maintain relatively uniform temperature conditions in the vapor space and to prevent an. excessive pressure drop in the vapor spacedue to decreasing atmospheric temperatures. l

' 4. In closed storage equipment containing a having been described vapor space above relatively volatile liquids and exposed to varying atmospheric temperatures whereby the temperature of the vapors varies, the vapor space being shut off from communication with the atmosphere over a definite temperature range only, the method of reducing evaporation losses, which comprises introducing steam into the vapor space to heat the same to approximately the maximum temperature to Vwhich the vapors are expected to rise during a givenv increment of time but below the upper limit of said temperature range, then cutting down the flow of steam into the vapor space until the temperature Within the vapor space approaches the. lower end of said range of temperatures, then reintroducing steam into the vapor space in amount sufficient to offset the reduction in temperature whereby the temperature within the vapor space is maintained at all times within the said range during varying atmospheric temperatures.

5. In closed storage. equipment containing a vapor space above: relatively volatile liquids and exposed to varying; atmospheric temperatures whereby the temperature of. the vapors varies, the vapor space being shut ofi from .communica-v tion with the atmosphere. overa definite temperature range only, rthe method of reducing evaporation losses, which comprises introducing heat of` steam. into the vapor space to heat the same to approximately the maximum temperature to which the vapors are expected to rise during a. given increment of time butbelow the vupper limit of said temperature range, then cutting down the now of steam. heat into the vapor space until the temperature within the vapor space approaches the lower end of said range of temperatures, then reintroducing steam heat into the Vapor space in amount sufficient t0 oifset `the reduction in temperature whereby the tem'- perature Within the vapor space is maintained` atv all times. within the. said range during varying atmospheric temperatures.

PAUL.. J. HARRINGTON. 

